Large-diameter single pile foundations of offshore wind turbines are always subjected to complex scour and disturbance of currents

as well as the vertical load (V) and horizontal load (H). Based on the Swipe loading method

the test of V-H combined loaded piles in sand is designed and completed in flume. The load-displacement curves and the bending moment of the pile shaft under both static and flowing states with different vertical loads are obtained. By dimensionless processing and fitting

the envelope of the V-H combined bearing capacity with consideration of the current effects is obtained. The results show that the total friction resistance of the pile side decreases due to the scouring action caused by the currents

and thus leading to decrease in the initial stiffness of the vertical load-displacement curve. When merely subjecting to the currents

the horizontal displacement and bending moment of the pile shaft are relative small

but they show significant increments when simultaneously subjecting to the combined action of horizontal force and the currents. An increase in the vertical force V on the pile head helps to improve the horizontal bearing capacity of the pile when the horizontal displacement of the pile is small. But when the horizontal displacement is large and V approaches to the limitation of the vertical bearing capacity Vu

the horizontal bearing capacity of the pile will be decreased due to the second order effects of gravity(P-Δ). The position of the maximum bending moment of the pile shaft is not significant changed with the flow state and V

which generally appears at the locations of 2–3 times the pile diameter below the mud line.